Incubation feeding in snow buntings: female manipulation or indirect male parental care?

Summary Male snow buntings regularly feed their mates on the nest during the incubation period. We removed males from 7 females at the start of incubation (Early Widows) and from 7 others when the eggs hatched (Late Widows) to experimentally assess the effects of incubation feeding on the behaviour of females and the reproductive success of both parents. Early Widows spent significantly more time off their nests than Late Widows and Controls. As a consequence, Early Widows had significantly longer incubation periods and a significantly higher proportion of them lost two or more eggs during development. There was no difference between Early and Late Widows in any index of reproductive success measured during the nestling period although significantly earlier brood reduction suggests that Early Widows were in poorer condition than Late Widows. Since both parents benefitted from incubation feeding by increased hatching success and shorter incubation periods, we conclude that this behaviour is an adaptive form of indirect parental care by males and is not the result of female manipulation.     

Quasi-parasitism in birds

Our view of avian mating systems has been revolutionised by the use of molecular tools that have provided evidence supporting theoretical predictions that extrapair paternity (EPP) and intra-specific brood parasitism (IBP) would be widely observed alternative mating strategies in socially monogamous species. Quasi-parasitism (QP) is a third type of alternative mating strategy, where a female lays an egg in another females nest and that egg is fertilised by the male partner at the parasitised nest. In contrast to both EPP and IBP, QP has been reported in only 12 species to date. We explore reasons for the apparent rarity of QP in birds and conclude that it is only likely to be adaptive in a fairly restrictive set of circumstances. We also review all of the evidence for the occurrence of QP in birds and find that it is far more limited than generally believed, as many apparent examples may be explained by rapid mate--switching or errors in molecular analysis of parentage. We suggest a number of criteria that need to be met for an unequivocal demonstration that QP has actually occurred.Communicated by: A. Cockburn     

Cadmium concentrations in human kidney in the UK: 1978-1993

Almost 2700 samples of human renal cortex have been collected from throughout the UK over a 16 year period from 1978 to 1993. The mean Cd concentration was 19 micrograms g-1 and the median 16 micrograms g-1. Smokers were, on average, about 5 micrograms g-1 higher than non-smokers. Cd increased from low concentration in the young to a maximum of 23 micrograms g-1 in middle age followed by a decrease in old age. Subjects who had died of renal disease had lower Cd concentrations. Geographical variations in the UK are small and the concentrations appear to be static over the 16 year period. Some 3.9% of the population had Cd concentrations > 50 micrograms g-1, the critical level at which beta 2-microglobulin appears in urine.     

Fecal indicator bacteria (FIB) levels during dry weather from Southern California reference streams

High levels of fecal indicator bacteria (FIB) in surface waters is a common problem in urban areas that often leads to impairment of beneficial uses such as swimming. Once impaired, common management and regulatory solutions include development of total maximum daily loads (TMDLs) and other water quality management plans. A critical element of these plans is establishment of a "reference" level of exceedances against which to assess management goals and TMDL compliance. The goal of this study was to provide information on indicator bacteria contributions from natural streams in undeveloped catchments throughout southern California during dry weather, non-storm conditions. To help establish a regional reference data set, bacteria levels [i.e. Escherichia coli (E. coli), enterococci and total coliforms] were measured from 15 unimpaired streams in 11 southern California watersheds weekly for one full year. Concentrations measured from reference areas were typically between one to two orders of magnitude lower than levels found in developed watersheds. Nearly 82% of the time, samples did not exceed daily and monthly bacterial indicator thresholds. E. coli had the lowest daily percent exceedance (1.5%). A total of 13.7% of enterococci exceeded daily thresholds. Indicator bacteria levels fluctuated seasonally with an average of 79% of both enterococci and total coliforms exceedances occurring during summer months (June to August). Temperature, at all sites, explained about one-half the variation in total coliforms density suggesting that stream temperatures regulated bacterial populations. Accounting for natural background levels will allow for management targets that are more reflective of the contributions from natural sources.     

Tactics of parasitic American coots: host choice and the pattern of egg dispersion among host nests

Summary I examined the tactics adopted by a conspecific brood parasite, the American coot (Fulica americana), and the degree to which these tactics reflect sources of mortality for parasitic eggs. Only 8% of parasitic eggs produced independent offspring, compared to a 35% success rate for non-parasitic eggs, and most mortality was due to egg-rejection by hosts or the consequences of laying eggs too late in the host's nesting cycle. Parasites usually laid parasitically before initiating their own nests and usually parasitized immediate neighbours. Parasites did not remove host eggs before laying their own egg, and egg disappearance in general was not more common at parasitized nests. I found no evidence for non-random host choice, either on the basis of stage of the host's nesting cycle or the host's brood size. The absence of adaptive host choice is likely a consequence of the fact that, due to host limitation, only a small proportion of parasites had meaningful variation among potential hosts to choose from. The pattern of egg dispersion among host nests by individual parasites appears to be a compromise between constraints imposed by host limitation and the increased success obtained from spreading eggs among nests. Most females laying fewer than five parasitic eggs laid them in a single host nest while females laying five or more eggs normally parasitized two or more hosts. An examination of egg rejection and survival rates showed that parasites would maximize success by laying a single egg per host nest, and the pattern of laying several eggs per host nest is likely a consequence of host limitation. However, no egg that was the fifth laid, or later, parasitic egg in a host nest was ever successful and this probably explains why most females laying five or more eggs parasitized more than one host.     

Mining of the forest and the time path of the price of timber

The paper analyzes the effect of transportation (site specific) costs and the effect of mining (depletion) of the forest on the time path of the price and of the net price of timber in two forestry models. The models differ in that one has zero costs and the other has positive costs. The analyses yield the standard mining theory results for certain cases. They also yield extentions of these results for cases with growth of the harvested trees and/or regeneration on the harvested land. The paper concludes, as one would expect, that the theory of the mine is useful in analyzing the time path of the price of timber.     

USING FIELD SCALE MODELS TO PREDICT PEAK FLOWS ON AGRICULTURAL WATERSHEDS1

The goal of this study was to develop a methodology for generating storm hydrographs at a watershed scale based on daily runoff estimates from a field scale model. The methodology was evaluated on a small agricultural watershed using the ADAPT field scale process model. A comparison of observed and predicted peak flows for 11 of the largest events that occurred in a three year period gave r² values of 0.84, 0.82, and 0.81 when the watershed was subdivided into 1, 5, and 10 sub watersheds. However, all other statistical measures improved when the watershed was subdivided into at least five sub watersheds. Guidelines need to be developed on the use of the procedure but it first needs to be evaluated on several watersheds that exhibit a range in sizes, land uses, slopes, and soil properties.     

Age dependence of potentially toxic elements (Sb,Cd, Pb,Ag) in human liver tissue from paediatric subjects

Toxic elements are present at low concentrations in the environment. This work was undertaken to investigate the age dependence of the liver content of selected elements in paediatric populations, as an index of internal exposure. Liver samples were collected at autopsy from 157 subjects, aged < 1 day to 6 years, as part of investigations on a possible role of Sb compounds in sudden infant death syndrome (SIDS). In addition to Sb, the concentrations of Ag, Cd and Pb were also determined by inductively coupled plasma mass spectrometry on the remaining digest. Comparison of 95% confidence intervals of the median concentrations of the four elements suggested that there were no differences between the two categories of cause of death, SIDS or those who had died of an identified disease. Cadmium, lead and antimony median concentrations were lower than corresponding values observed in adult populations. Silver concentrations were significantly higher at birth and decreased with age. Cadmium levels were almost negligible in neonates and infants, but increased in older children. The finding of non-negligible concentrations of both Ag and Pb in neonatal liver provides further direct evidence that these elements cross the human placental barrier. The reported data, by far the largest collection observed in subjects less than 1 year old, are the result of exposure, during pregnancy and in early childhood, to present levels of these elements in the environment. They can serve as a reference to compare post-mortem values from individuals or groups of subjects in this age range when an exposure risk is suspected and to highlight trends in human exposure.     

THE IMPACT OF RUNOFF GENERATION MECHANISMS ON THE LOCATION OF CRITICAL SOURCE AREAS1

ABSTRACT: Identifying phosphorus (P) source areas and transport pathways is a key step in decreasing P loading to natural water systems. This study compared the effects of two modeled runoff generation processes ‐ saturation excess and infiltration excess ‐ on total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations in 10 catchment streams of a Catskill mountain watershed in southeastern New York. The spatial distribution of runoff from forested land and agricultural land was generated for both runoff processes; results of both distributions were consistent with Soil Conservation Service‐Curve Number (SCS‐CN) theory. These spatial runoff distributions were then used to simulate stream concentrations of TP and SRP through a simple equation derived from an observed relation between P concentration and land use; empirical results indicate that TP and SRP concentrations increased with increasing percentage of agricultural land. Simulated TP and SRP stream concentrations predicted for the 10 catchments were strongly affected by the assumed runoff mechanism. The modeled TP and SRP concentrations produced by saturation excess distribution averaged 31 percent higher and 42 percent higher, respectively, than those produced by the infiltration excess distribution. Misrepresenting the primary runoff mechanism could not only produce erroneous concentrations, it could fail to correctly locate critical source areas for implementation of best management practices. Thus, identification of the primary runoff mechanism is critical in selection of appropriate models in the mitigation of nonpoint source pollution. Correct representation of runoff processes is also critical in the future development of biogeochemical transport models, especially those that address nutrient fluxes.